The present invention generally relates to methods, apparatuses, and devices for cooling high-power density electronics, including but not limited to memory modules of computers. More particularly, this invention relates to cooling methods, apparatuses, and devices that utilize a heatpipe to cool a computer memory module.
Computer memory has evolved from a small number of integrated memory chips to a multi-module subsystem. Aside from the increased footprint, the power consumption of system memory has also increased far beyond the levels found in legacy memory solutions. A prominent role in the overall power consumption of a system memory module is played by the actual mode of operation or state of the Dynamic Random Access Memory (DRAM) chips on the module. For example, in no-operation situations in which no transactions occur and only the memory internal clocks are running, the power consumption is only a fraction of that during a four-way interleaved read, during which data are streamed out into the bus from all four internal banks of the memory components. With every generation of double data rate (DDR) memory, the number of prefetched bits is also increasing (for example, DDR3 currently prefetches eight bits on every access), which extends the minimum data that are output on the bus during each burst. Any mandatory increase in the burst length increases the number of total transactions and, therefore, the power needed for sustaining them. This escalation of power has evolved into a limitation of the maximum number of bursts within a defined time window (tFAW) for the purpose of thermal relaxation under full load.
Historically, only the Rambus DRAM memory technology (Rambus, Inc.) had a power consumption high enough to thermally challenge the DRAM components. This was counteracted by supplying heat spreaders for the DRAM components, whereas SDRAM and later DDR modules were primarily built without any thermal management add-ons. In the enthusiast market, heat spreaders for memory were introduced in 2001 by Mushkin Enhanced Memory Systems and, concurrently, by Thermaltake as an original equipment manufacturer for a number of enthusiast memory suppliers. However, modern memory with increasing clock frequencies can incur power consumption and heat dissipation in excess of that found only a few years ago in commodity memory systems. As a result, heat spreaders are becoming more and more common and are becoming part of the DRAM standard, at least to the point where their presence or absence is catalogued in the module's electronic data sheet, namely, the serial presence detect (SPD) read-only memory (ROM) on the module.
An inherent drawback of conventional memory heat spreaders is that their physical size does not exceed that of the memory module; as a result, while small hot-spots are dissipated over an increased surface, the overall dissipation area of the heat spreader is not increased compared to the module itself. Thermal dissipation is, however, limited by the radiator surface area and the temperature delta to the environment. Therefore, presuming a constant environmental temperature, the only way to lower the source temperature is to increase the radiator area size. However, within the confined space available for each memory module on a motherboard, passive heat conductance across a solid structure becomes the primary limitation for moving heat away from its source. It is clear, therefore, that an active removal of heat from the memory would be highly beneficial for its thermal management.
In cooling solutions for central processors (CPU) and graphics processors (GPU), as well as other high power density electronics, heatpipe technology has been used for several years. Heatpipes operate based on the principle of using a pipe filled with water (or another suitable coolant) under partial vacuum conditions. The partial vacuum within the pipe can be selected to lower the boiling point of the water to a desired temperature. At any location within the pipe at which the desired temperature is exceeded, the water will boil and, in the process of changing from the liquid to the gaseous (vapor) phase, absorb heat energy. The resultant vapor rises within the heatpipe and typically condenses at a remote end of the pipe. Condensation can be promoted with a wick or a sintered porous surface within the pipe that increases the condensation surface and capillary action, thereby promoting the return of liquid water to the heat source.
As memory modules have become more thermally challenged due to increased power consumption, the design of the memory subsystem on most motherboards has changed little to accommodate much in terms of thermal management solutions because of space constraints. The high operating frequencies of high performance memory modules are particularly affected since the power consumption increases with frequency, and to achieve higher frequencies the voltage often must also be raised. Higher power consumption increases the junction temperature on the memory die, which in turn slows down signal propagation along the interconnect of the memory die, thereby reducing the maximum attainable frequency of the memory and potentially increasing the error rate.
In view of the above, in high performance memory modules, and particularly those using increased supply voltage, thermal management is becoming a crucial aspect of overall performance. Because of the limited space between memory modules, the cross-sectional area of any heat-dissipating device must be very small, exacerbating the limitations of passive cooling techniques. Furthermore, transferring heat to fins is similarly hampered by the same limitations of the fin design and passive conductance limitations. A solution to this aspect of the problem has been to use active cooling techniques, for example, forced water cooling. However, forced water cooling is not practical for all implementations, especially since it requires a considerable amount of additional equipment, for example, radiators, tubing and pumps.